A surface energy driven dissolution model for immiscible Cu-Fe alloy

Abstract

Cu-Fe alloy processed by conventional preparation methods has serious large-scale composition segregation or spatial separation of individual Cu and Fe phases prior to solidification. For immiscible Cu-Fe alloy, a homogeneous melt is the prerequisite to obtain the subsequent uniform solidification microstructure. In this paper, the uniform metastable immiscible Cu100−xFex alloys (x=10, 20, 30, 40wt%) were prepared by arc-melting. The results indicated that with increasing melting times, the initial aggregated Fe-rich melt gradually dissolves into the bulk copper matrix and a homogeneous melt is obtained. Herein a thermodynamic model was constructed to discuss the surface energy driven melting process and the formation of uniform Cu-Fe alloy. During melting process, if the radius of detached liquid Fe-rich droplet is less than the calculated critical radius, the surface energy is high enough to compensate for the partial molar excess Gibbs energy of iron, thereby leading to the spontaneously dissolution of detached liquid Fe-rich droplet into the bulk liquid. As a result, the aggregated Fe-rich melt dissolves step by step eventually forming a homogeneous melt. After subsequent solidification, the immiscible Cu-Fe alloy exhibits homogeneous microstructure. The rapid melt quenching experiments are further performed to validate the proposal model. The results provide strong evidence and support for the surface energy driven dissolution model. The findings give us a basic understanding for the evolution of melting process in other immiscible alloys.